Electrophotographic copying paper

ABSTRACT

Electrophotographic copying paper having a coating applied on the paper support or substrate thereof, said coating comprising naphthalenesulfonate formaldehyde condensate of the formula:   (WHEREIN R is H, CH3 or C2H5, M is Na, K, Li or NH4, and n is an integer of 1 to 20), said coating imparting low surface resistance properties to said support.

United States Patent [191 Sakaguchi et al.

[4 1 Sept. 9, 1975 ELECTROPHOTOGRAPHIC COPYING PAPER [75] Inventors: Kahei Sakaguchi; Noboru Moriyama; Hirotaka Takemoto, all of Wakayama, Japan [30] Foreign Application Priority Data Dec. 19, 1972 Japan 47-127473 [52] U.S. Cl 96/l.5; 96/1.7; 117/155 L; 117/201 [51] Int. Cl G03g 5/04 [58] Field of Search 117/155 L, 154; 96/1.7, 96/1.5

[56] References Cited UNITED STATES PATENTS 3,121,708 2/1964 Engclmann 117/155 L 3,240,594 3/1966 Cassiers r 96/l.5 3,240,597 3/1966 Fox 96/l.5

Primary Examiner-Norman G. Torchin Assistant Examiner-John L. Goodrow Attorney, Agent, or FirmWoodhams, Blanchard & Flynn [57] ABSTRACT Electrophotographic copying paper having a coating applied on the paper support or substrate thereof, said coating comprising naphthalenesulfonate formaldehyde condensate of the formula:

(wherein R is H, CH or C H M is Na, K, Li or NH and n is an integer of 1 to 20), said coating imparting low surface resistance properties to said support.

10 Claims, No Drawings ELECTROPI'IOTOGRAPHIC COPYING PAPER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to electrophotographic copying paper having an electrically conductive paper support or substrate, and a method of making same. More particularly, this invention comprises treating the paper base or substrate of electrophotographic copying paper with naphthalenesulfonate formaldehyde condensate to impart low-resistance properties thereto.

2. Description of the Prior Art Electrophotography is a well-known photographic reproduction technique utilizing the combined characteristics of photoconductivity and electrostatic phenomenon. It is, in principle, based on the theory of Xerography invented by C. F. Carlson.

Electrophotographic copying paper is prepared by applying on a low-resistance base or substrate a photoconductive powder dispersion or photoconductive sensitive layer comprising zinc oxide powder dispersed in a binder such as, for example, silicon resin or unsaturated polyester, so as to be capable of forming electrostatic latent images through the action of light. It is required that the surface resistance of the low-resistance base or substrate be within the range of from l to l0 .0, (ohms) when the relative humidity of the ambient atmosphere is from 20 to 90 percent. It is believed that if the surface resistance is outside that range, a good image cannot be obtained.

This invention has for its object to provide an improved electrophotographic copying paper in which the base or substrate has applied thereto a low resistance processing agent that can satisfy the above mentioned requirements.

As processing agents for preparing conductive processed papers, there have been used heretofore anionic water-soluble polymers such as poly(vinylbenzyltrimethylammonium chloride) as disclosed in US. Pat. Nos. 3,620,828 and 3,01 1,918. More recently, oligostyrenemaleic anhydride copolymers have been used as more effective agents.

SUMMARY OF THE INVENTION According to the invention, there is provided an improved electrophotographic copying paper in which the base or substrate has applied thereto a coating of naphthalenesulfonate formaldehyde condensate of the formula:

(wherein R is H, CH or C H M is Na, K, Li or NH and n is an integer of from 1 to The condensate is applied to the base or substrate in the form of an aqueous solution or aqueous dispersion thereof which is then dried so that the condensate is present on the base or substrate in the form of fine particles adhering to the surface of the base or substrate.

The naphthalenesulfonate formaldehyde condensate according to the present invention is applied in an amount of 0.1 to 10 g/m preferably 1 to 3 g/m calculated as the solids, based on the surface area treated of the paper base or substrate. The aqueous solution or dispersion of said condensate is usually applied by itself to the base paper, but if required, a known additive or additives which have been generally used heretofore, such as inorganic metal salts, surfactants, moisture absorbents or polyelectrolytes can be used in admixture with said condensate.

Various types of coaters such as roll coaters, sizing presses, knife coaters or bar coaters can be used for applying said aqueous solution or dispersion to the base paper.

In applying the naphthalenesulfonate formaldehyde condensate, it is usually desirable, as aforementioned, to apply it in the form of a water solution when said condensate is water-soluble or in the form of aqueous dispersion when said condensate is dispersed in water with the aid of a dispersant.

The conductive processed base paper obtained by applying to the base paper the processing agent of the present invention is low in surface electric resistance over a wide humidity range, and the electrophotographic copying paper produced by using such processed paper can produce high-quality images.

After processing the base paper or substrate with the processing agent, in accordance with this invention, a photoconductive layer or film is applied on top of the processing agent and adhered to the substrate to form the completed electrophotographic copying paper. The photoconductive layer comprises a dispersion of organic or inorganic photoconductive substance dispersed in a resinous binder having relatively high electrical resistivity. It is preferred to use photoconductive zinc oxide as the photoconductive substance. The binder resin can be selected from any of those suitable for preparing such photoconductive layers. It will be understood that the present invention does not relate to any discovery relating to the composition of the photoconductive layer. This can be selected from compositions suitable for this purpose. A detailed description thereof is believed to be unnecessary because suitable compositions are well known.

Among the naphthalenesulfonate formaldehyde condensates that can be used in the present invention are aor ,B-naphthalenesulfonate formaldehyde condensates in which R is H, or naphthalene sulfonate formaldehyde condensates in which R is an alkyl group with l to 2 carbon atoms, such as methyl or ethyl group, and the like. The preferred condensate is ,B-naphthalenesulfonate formaldehyde condensate. Another preference is for compounds in which n is from 4 to 12. These compounds, for example, the sodium salt of formaldehyde condensate of ,B-naphthalene sulfonic acid are known compounds. They can be synthesized in, for instance, the following way.

288 Grams 1 mol) of ,B-naphthalenesulfonic acid, 30 grams (0.3 mol) of 95 percent sulfuric acid and 48 grams of water are put into a four-necked flask. A substantial portion of the B-naphthalenesulfonic acid is dissolved at to C, and then 17.2 grams of an aqueous solution containing 35.8 wt. percent formaldehyde is added to the solution. While maintaining the mixture at 80 to 85C, further amounts of 17.2 grams of said formaldehyde solution are added after 1, 2 and 3 hours, respectively, so that the total amount of formaldehyde solution added is 688 grams (0.82 mol). After the completion of the addition of formaldehyde solution, the mixture is heated to 95 to 100C in 20 Specimen Nos. 6 to 8 are comparison specimens employing different metal salts of the condensate. As is apparent from the table, the surface resistance characteristics of the treated base papers, under different huminutes and reacted at that temperature for a period of midity conditions, obtained from the specimens of the 7 /2 hours. Then, an aqueous solution of calcium carpresent invention are far better than those obtained bonate is added to perform liming, and then sodium from the comparison specimens. carbonate is added to the hot filtrate to form the so- It was also confirmed by hand touch that the prodium salt. The insoluble inorganic salts are filtered cessed papers prepared according to the present invenaway, and the filtrate is evaporated to obtain the sotion remain nonsticky even in a highly humid atmodium salt of B-naphthalenesulfonic acid formaldehyde sphere. condensate (11 6, R=H, M=Na). Then, a zinc oxide resin binder composed of a uni- The invention is further described by reference to the form mixture of 4 parts by weight of zinc oxide powder following illustrative examples. and 1 part by weight of resin binder (unsaturated poly- EXAMPLE 1 ester having an average molecular weight of 3,000) obtained by reacting 3,3-di(4-,8hydroxypropoxyphenyl Aqueous solutions of the respective low-resistance propane) with fumaric acid, was applied in an amount processing agents (conductive processing agent) listed of g/m on the conductive processed papers (Speciin the following table were applied by a knife coater on men Nos. 1 to 5) according to the present invention to one side of a commercial high-quality cellulosic fiber 20 produce electrophotographic recording papers. The paper (weighing 70 g/m) such that said agent was apimage-forming characteristics of the thus obtained replied in amount of 2 g/m calculated as the solids, cording papers were examined by testing them in a based on the treated area of the paper. After drying the commercial electrophotographic copying machine. treated paper under reduced pressure, specimens of the Vivid and clear images can be obtained with any of treated paper were placed in desiccators having 20 perthese recording papers. cent relative humidity (RH) and 60 percent relative hu- Comparative Example midity, respectively, and were allowed to stand therein for 24 hours. Thereafter, the specimens were taken out Conductive processed papers were prepared accordof said desiccators and their surface resistances were ing to the same method and under the same conditions measured by using as measuring electrodes, Model as in the above-described example by using two repre- RC-OZ manufactured by Kawaguchi Denki Seisakujo. sentative types of commercial conductive treating The results are shown in Table 1 below. The processing agents. The surface resistance of the thus obtained proagents were used in the form of 30 wt. percent aqueous cessed papers at 20 and 60% RH was measured. The solutions. results are shown in Table 2 below in comparison with Table 1 Specimen Surface resistance of No. Processing agent processed paper (ohms) RH 20% RH 60% Examples 1 Sodium B-naphthalenesulfonate formaldehyde 7.0 X 10 5.5 X 10 of the condensate (n 6) Present 2 Ammonium B-naphthalenesulfonatc formaldehyde 5.0 X 10 3.8 X 10 Invention (n 6) 3 Lithium B-naphthalencsulfonate formaldehyde 1.0 X 10 8.9 X 10 condensate (n 6) 4 Potassium fi-naphthalenesulfonate formaldehyde 7.2 X 107 6.5 X 107 condensate (n 6) 5 Sodium ,B-naphthalenesulfonatc formaldehyde 9.8 X 107 5.5 X 10 condensate (n 10) Comparative 6 Magnesium B-naphtlialenesulfonate formaldehyde 1.] X 10 8.7 X 10 Examples condensate (n 6) 7 Strontium B-naphthalenesulfonate formaldehyde 13 X 10'" 8.0 X 10" condensate (n 6) 8 Zine Bmaphthalenesulfonate formaldehyde 2.5 X 10" 8.0 X 10 condensate (n 6) 9 Not treated 3.4 X 10 1.3 X l0 1n the above table, p im n 1 IO 5 are specimens the test results of Specimen No. l of the present invenprepared according to the present invention, whereas tion.

Table 2 Specimen Treating agent Surface resistance of No. treated paper (ohms) RH 2O RH Yr Comparal0 Poly(viny1benzyltri tive methylammonium 1.8 X 10 1.2 X 10" Examples chloride)* 1 l Poly(styrene sodium 8.4 X 10 6.0 X 10 sulfonate Present 1 Sodium fl-naphthalene- Invention sulfonate 7.0 X 10 5.5 X 10 formaldehyde condensate (n 6) Note) Tradename ECR 34 mfd. by Dow Chemical Co. **Tradename Oligo Z mfd. by Tomoegawa Paper Mfg. (1).. Ltd.

These results show that the treating agents according to the present invention provide as good or better surface resistance characteristics than the best commercial products.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In an electrophotographic copying paper comprising a support having on one surface thereof a photoconductive layer comprising a mixture of photoconductive substance and a film-forming resin binder, the improvement which comprises:

said surface of said support has applied thereon, un-

derneath said photoconductive layer, a coating of naphthalenesulfonate formaldehyde condensate of the formula 3 b O 3 M wherein R is H, CH or C H M is Na, K, Li or NH and n is an integer of l to 20, in an amount effective to reduce the surface electrical resistance of said support to within the range of to 10 ohms.

2. An electrophotographic copying paper according to claim 1, in which said coating is applied on said surface in an amount of from 0.1 to 10 g/m based on the area of said surface.

3. An electrophotographic copying paper according to claim 1, in which said coating is applied on said surface in an amount of from 1.0 to 3.0 glm based on the area of said surface.

4. An electrophotographic copying material according to claim 1, in which said support is paper made of cellulosic fibers.

5. An electrophotographic copying material according to claim 2, in which R is H and M is Na.

6. An electrophotographic copying material according to claim 1, in which n is from 4 to 12.

7. A method of producing paper processed to have a surface electrical resistance in the range of about 10 to about 10 ohms, which comprises applying to a surface of the paper a coating of an aqueous solution or dispersion of naphthalenesulfonate formaldehyde condensate of the formula wherein R is H, CH or C 11 M is Na, K, Li or NH and n is an integer of 1 to 20 and drying said coating.

8. A method according to claim 7, in which said coating is applied on said surface in an amount of from 0.1 to 10.0 g/m calculated as the solids, based on the area of said surface.

9. A method according to claim 7, in which said coating is applied on said surface in an amount of from 1.0 to 3.0 g/m", calculated as the solids, based on the area of said surface.

10. A method according to claim 7, including the further step of applying on said surface having said dried coating thereon, a mixture of photoconductive substance and film-forming resin binder to form a photoconductive layer. 

1. IN AN ELECTROPHOTOGRAPHIC COPYING PAPER COMPRISING A SUPPORT HAVING ON ONE SURFACE THEREOF A PHOTOCONDUCTIVE LAYER COMPRISING A MIXTURE OF PHOTOCONDUCTIE SUBSTANCE AND A FILM-FORMING RESIN BINDER, THE IMPROVEMENT WHICH COMPRISES: SAID SURFACE OF SAID SUPPORT HAS APPLIED, UNDERNEATH SAID PHOTOCONDUCTIVE LAYER A COATING OF NAPHTHALENESULFONATE FORMALDEHYDE CONDENSATE OF THE FORMULA
 2. An electrophotographic copying paper according to claim 1, in which said coating is applied on said surface in an amount of from 0.1 to 10 g/m2, based on the area of said surface.
 3. An electrophotographic copying paper according to claim 1, in which said coating is applied on said surface in an amount of from 1.0 to 3.0 g/m2, based on the area of said surface.
 4. An electrophotographic copying material according to claim 1, in which said support is paper made of cellulosic fibers.
 5. An electrophotographic copying material according to claim 2, in which R is H and M is Na.
 6. An electrophotographic copying material according to claim 1, in which n is from 4 to
 12. 7. A method of producing paper processed to have a surface electrical resistance in the range of about 106 to about 109 ohms, which comprises applying to a surface of the paper a coating of an aqueous solution or dispersion of naphthalenesulfonate formaldehyde condensate of the formula
 8. A method according to claim 7, in which said coating is applied on said surface in an amount of from 0.1 to 10.0 g/m2, calculated as the solids, based on the area of said surface.
 9. A method according to claim 7, in which said coating is applied on said surface in an amount of from 1.0 to 3.0 g/m2, calculated as the solids, based on the area of said surface.
 10. A method according to claim 7, including the further step of applYing on said surface having said dried coating thereon, a mixture of photoconductive substance and film-forming resin binder to form a photoconductive layer. 